Australian Patent No. 579,830 to Trowland describes a tipping apparatus having an arrangement for tipping the box body of a trailer with respect to its chassis. An inflatable bag is inflated to tilt the box body by coupling the bag to the exhaust pipe of the towing vehicle. The inflatable bag is substantially cylindrical and has its ends mounted to the box body and the chassis via upper and lower load transmitting end plates. The bag is made from blanks of flexible material joined by seams and has its ends fixed to the end plates via tabs joined to the bag and having their free ends stapled or otherwise secured to the end plates.
While this bag is relatively simple to construct and can be easily mounted to the box and chassis, stresses created during inflation are unevenly distributed causing excessive stress at the seams of the bag. This shortens the life of the bag. In addition, on deflation the bag tends to fold in a disorderly manner and can in parts extend beyond the edges of the load transmitting plates. Chafing of the protruding parts of the bag can occur thereby shortening the life of the bag.
Another problem with this bag is that as a consequence of the fitting arrangement, that is via tabs at each end of the bag, there is a tendency for the bag to rotate on the plates and this can break the tab joins and reduce the life of the bag.
A still further problem is that for conventional vehicles such as pick ups, utility trucks and trailers, in order to achieve a useful tipping angle, of say 50.degree., with the Trowland bag it is necessary to make the bag excessively large.
In Australian Patent Application No. 18662/88 to Beer there is disclosed an incline lift assembly where Beer has specifically set out to overcome the disadvantages of the Trowland arrangement. In order to provide a bag which deflates in an orderly manner the bag according to Beer has when inflated, a cross-section which diminishes in one direction so that the narrowest portion of the bag deflates within the periphery of the broadest portion. Unfortunately, all the Beer proposals sacrifice the simplicity of the Trowland bag in order to overcome the abovementioned problems. Each of the Beer bag arrangements are complex and expensive.
In order to lift to high angles the Beer proposal includes a complicated arrangement of hinges and scissor struts in order to maintain the end plates parallel while the tip box is hinged to the rear end of the upper end plate. This arrangement necessarily reduces the amount of force that can be applied directly to a load.
U.S. Pat. No. 4,572,579 to Saito describes a dump apparatus having a bag which is substantially trapezoidal in shape when inflated. The bag is mounted to end plates and is confined when inflated by flexible strut members in order to prevent excessive lateral inflation of the bag. The struts also assist in distributing stress and thereby concentrating the inflation in the forward and rear direction rather than laterally. In order to achieve high tipping angles with this arrangement it is necessary to hinge the tip box to the rearward end of the upper plate so that the plates remain parallel during inflation. As for the similar arrangement of Beer this necessarily reduces the amount of force that can be applied to the load.
It is therefore a principal object of the present invention to overcome or at least alleviate some of the problems associated with the aforementioned prior art.